Tunneling sensors may use a bias voltage applied between an electrode tip and a conducting sample. When the tip and the sample are brought to within a few Angstroms (Å) of each other, a tunneling current may flow due to quantum mechanical tunneling effects. Because the tunneling current may depend exponentially on the separation between the electrode tip and the conducting sample, the distance between the electrode tip and the conducting sample may be measured to within, for example, 10−3 (Å).
E. Boyden et al., “A High-Performance Tunneling Accelerometer” MIT Term Project Paper 6.777, Introduction to Microelectromechanical Systems, Spring 1999, discusses a tunneling sensor based on an at least two-layer structural configuration, i.e. adjacent electrode tips are located in different wafer layers, which may complicate the manufacture process and involve higher cost. If made from silicon, for example, microelectromechanical tunneling sensors may require a metal contact since the native oxide of silicon may be too thick to allow tunneling. (The native oxide results when silicon is exposed to air, thereby forming an insulator layer that prevents the flow of tunnel current). Furthermore, such a multi-layer structural configuration may require a separate proof mass for each dimension measured by the sensor—for example: one proof mass for a one-dimensional sensor (a linear accelerometer) or two proof masses for a two-dimensional sensor (an angular accelerometer) or three proof masses for a three-dimensional sensor (a gyroscope).
A tunneling current sensor fabricated using bulk silicon micro-machining technology and a boron etch-stop dissolved wafer process is discussed in Chingwen Yeh, “A Low Voltage Tunneling-based Silicon Microaccelerometer”, University of Michigan Research Project Paper. Such a tunneling current sensor may likewise be difficult and costly to manufacture, as well as require multiple proof masses for two- and three-dimensional measuring devices.